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I have a ZXR400 L model 1993 which has done 15’000 miles it isn’t pushing the coolant from the overflow back to the radiator, after riding the water is boiling in the overflow a small amount is dripping out the overflow pipe but nothing much at all stops as soon as it has called a bit. I have recently filled the radiator (up to the top) and was wondering if this could be the reason why? It’s not running hot and the oil is very clean no mayonnaise or smoke (checked for the obvious signs of head gasket). Has anybody got any idea’s?

yet again, are you putting any anti-freeze in? or are you just filling it up with water?

Yes it has anti freeze in it

what does it matter if he is using anti-freeze or not, its a suspected coolant leak.

Once the water is forced into the tank it cant go back into the radiator. So at any time after a ride once it has all cooled the water level in the rad isn't going to be brimming.

yeap!!! that 'll be the head gasket then. mine done the same, no oil in the water to find any cream. using water and blowing it back in the expansion tank.

Don't let it get hot my friend or you'll need to skim the head, mine went between cyclinders 1 & 2. it's a days work and the gasket it cost about 15 all i and you'll need some new exhaust gaskets too about 2 each.

some water will always be forced into the tank, until the system finds a point at which there is enough air space in the circuit for the water to heat without meeting the lift pressure of the rad cap.

Bit of an update not sure if this still means the head gasket or not. It is sucking the water back from the expansion tank to the rad (system correctly pressureised) and is fine when the bike is moving, however as soon as i get to traffic or do any town ridding it heats up, any idea's? Not sure if the fan is kicking in can't her anything and doesn't seem to be on when i stop could this be the reason for the temperature?

Its normal for the bike to heat up in town and slow moving traffic but how far does it go up the temperature scale?

If i left it, it would go all the way and there is still no fan kicking in. If i going along at a normal pace it sits fine just when i slow down.

Sounds almost normal apart from the fan not kicking in.

Northern ANdy wrote:what does it matter if he is using anti-freeze or not, its a suspected coolant leak.

anti-freeze doesn't just stop it freezing in winter, it also raises the boiling point. if there's just water in it, it will boil sooner, and as soon as it starts boiling it will find a way to leak out.

...is i suspect where caz was coming from.

i'd also suggest checking the fan circuit and particularly the fan switch in the rad.

- unplug the lead to the fan switch, short the two terminals together and turn the ignition on. If the fan comes on, the rest of your circuit is ok.

- if you have a test meter you can take the switch out amd suspend it in a pan of water - it should be open circuit cold, then at a particular temperature it will go closed circuit. I've also done it with the radiator off the bike and the switch fitted by just pouring a kettle full of water through it.

my fan fuse sometimes blows, I'd check tha first.

Re: the antifreeze I just thought Caz was trying to suggest this was the problem.

suppose i ought to get round to replying

Re antifreeze - you're completely correct with what I was implying. Anti-freeze raises the boiling point of water. If you arent running any in your system, it could explain why it was running hot!

and Andy - nope, lack of antifreeze in the system isnt going to cause a coolant leak, but it could be a contributing factor to it running hot.

It has anti-freeze in it, it pushes the coolant out the system into the expansion tank once it has cooled down it takes it back to the rad. I went out last night didn't go in any real traffic and sat just under the half way mark the whole time however it still pushed some out the the expansion, does this sound ok and i have just never noticed it or is it a problem?

ross59 wrote:It has anti-freeze in it, it pushes the coolant out the system into the expansion tank once it has cooled down it takes it back to the rad. I went out last night didn't go in any real traffic and sat just under the half way mark the whole time however it still pushed some out the the expansion, does this sound ok and i have just never noticed it or is it a problem?

this is what should happen, and it's why there is an expansion tank - to allow for the expansion of the coolant when it gets hot.

only thing i'd say is there should always be coolant in your expansion tank. if it all disappears into the engine when cold you need to top it up!